The present invention relates to a bearing structure and a manufacturing method thereof. More specifically, the invention relates to a bearing structure comprising a divided-type rolling bearing suitable for supporting a shaft such as a crankshaft and a camshaft in an engine and a housing for supporting the rolling bearing, and also relates to a manufacturing method thereof.
In an engine of an automobile, a ship or others, a bearing for supporting a crankshaft for converting a reciprocal movement of a piston into a rotational movement is disposed between counterweights or between a counterweight and a con rod larger end portion, and therefore a divided-type bearing (two-division bearing) divided circumferentially into two sections has been used as it.
A slide bearing has heretofore been used as the above supporting bearing. However, in recent years, there is an increasing demand for engines having a less fuel consumption, and therefore it has been proposed to use, instead of the slide bearing, a divided-type rolling bearing (two-division rolling bearing) divided in a circumferential direction.
The divided-type rolling bearing comprises, for example, a pair of two-division outer rings, a plurality of rollers so mounted as to be able to roll on inner side surfaces of the two two-division outer rings, and a pair of two-division cages holding the rollers such that the rollers are arranged at generally-equal intervals in the circumferential direction. A crankshaft is internally fitted, as an inner ring member, to the rolling bearing.
By the way, in the above divided-type rolling bearing, circumferential end faces of the pair of two-division outer rings are held against each other to form mating surfaces, and in the mating surface, a radial offset may develop at the opposed outer ring both end portions. As a result, a radially inwardly-projecting step is formed at the mating surface, and there is a problem that vibration and noise are generated when the roller passes this step.
Therefore, in order to eliminate effects of such step, it has been proposed to apply processing such as the formation of inclined surfaces at the circumferential end portions of the outer rings (for example, see Patent Literatures 1 to 2).
A two-division- outer ring 30 formed by curving a strip-like metal sheet into a generally semicircular shape is disclosed in Patent Literature 1, and as shown in FIG. 15(a), it is described that at least one circumferential end of the two-division outer ring 30 is formed into a convex-concave shape including an inclined portion 31 inclined relative to a line extending along an axial direction and an inclined portion 32 inclined toward the opposite side of the inclined portion 31. Also, it is described that a corner portion 33 of the one circumferential end disposed at the inner side surface is formed into a round shape (see FIG. 15(b)).
In Patent Literature 2, as shown in FIG. 16, there is disclosed a bearing in which butting portions of both circumferential ends of two-division outer rings 40 are constructed by fitting a V-shaped convex portion 41, projecting in a circumferential direction, and a V-shaped convex portion 42, recessed in the circumferential direction, to each other. Circumferential both end portions of an inner peripheral surface of each outer ring on which rollers rolls are inclined to become closer to an outer peripheral surface toward the respective end edges, thereby gradually decreasing a radial thickness dimension toward the circumferential end edge.
In the bearings described in Patent Literatures 1 and 2, it is mentioned that the development of a step can be prevented by the above rounded corner portion or the above inclinations.
On the other hand, in the above divided-type rolling bearing, there are fears that the divided outer ring may rotate in the circumferential direction relative to the housing and that it may move in the axial direction. Above all, in the above divided-type rolling bearing, for example, in the case where a housing made of aluminum alloy is used as the housing in order to achieve a lightweight design, a larger difference in coefficient of linear expansion develops between the housing and the outer ring, depending on the kind of a material used for the outer ring. Therefore, there are fears that the rotation of the outer ring in the circumferential direction and the movement of the outer ring in the axial direction are more liable to occur with a temperature rise during the operation of an engine.
Therefore, there has been proposed a divided-type rolling bearing device (Patent Literature 3) constructed such that in order to suppress the rotation of an outer ring together with a shaft when in use, an outwardly-projecting rotation prevention portion is formed on an outer peripheral surface of the outer ring by a press-shaping processing, and the rotation prevention portion is fitted in a hole formed in a bearing housing.
Furthermore, in the above divided-type rolling bearing, the circumferential end faces of the pair of two-division outer rings are held against each other to form the mating surfaces, and in the mating surface, a radial offset may develop at the opposed outer ring both end portions, depending on a processed condition of a fitting surface of the housing for receiving the outer ring or on an error in the mounting of the outer ring on the housing. As a result, a radially inwardly-projecting step is formed at the mating surface, and there are fears that vibration and noise may be generated when the roller passes this step and that premature damage such as cracking, chipping and separation of the rollers and outer ring may occur.
Therefore, in order to eliminate effects of such step, it has been proposed to apply processing such as the formation of inclined surfaces at the circumferential end portions of the outer ring (for example, see Patent Literature 4).
In Patent Literature 4, there is disclosed a rolling bearing comprising an outer ring having division surface portions combined together, and a cage which receives a plurality of rollers for rolling along an inner peripheral surface of the outer ring and is mounted on the inner peripheral surface of the outer ring. It is described that each division surface portion of the outer ring has a surface inclined relative to an axial direction and that the inner peripheral surface side of the division surface portion has an inclined surface inclined at least in a radial direction and gradually decreasing in thickness toward a distal end. In the bearing described in Patent Literature 4, it is mentioned that the generation of a step can be prevented by the above inclined surface.
Further, it has been proposed to vary a radial dimension of an outer ring in accordance with a circumferential position (for example, see Patent Literature 5).
In Patent Literature 5, there is described a rolling bearing in which an outside diameter shape of each of two halves of the divided outer ring is formed into a half circle obtained by dividing one true circle into two, and an inside diameter shape of the two halves of the divided outer ring is formed into a partial circle having a deformed portion at part of a half circle obtained by dividing one true circle into two, and the center of the partial circle is offset a predetermined amount from the bearing center.
Patent Literature 1: JP-A-2005-337352 Publication
Patent Literature 2: JP-A-2006-125606 Publication
Patent Literature 3: JP-A-2006-329382 Publication
Patent Literature 4: JP-A-2006-336765 Publication
Patent Literature 5: JP-A-2006-258138 Publication